Aluminum-beryllium alloy and method of treatment



Patented .June 11, 1929.

UNITED STATES ROBERT S. ARCHER AND WILLIAM L. FIN K, OF

PATENT OFFICE.

CLEVELAND, OHIO, ASSIGNOBS T ALU- 'IION OF PENNSYLVANIA.

ALUMINUM-BERYLLIUM ALLOY AND METHOD OF TREATMENT.

No Drawing.

" The invention relates to aluminum base alloys containing beryllium,one object being to provide a method of heat-treating such alloys toimprove their physical properties,

and another to provide improved aluminumberyllium alloys which havesubstantial advantages without as well as with heat-treatnient.

Because of its low, density,beryllium is a desirable alloying elementfor many purposes for which light aluminum base alloys are used, butbecause of its present high cost,

beryllium cannot be used in large quantities as an alloying constituentin competition with less expensive alloying constituents.

We have discovered, however, that by alloying relatively smallquantities of beryllium with aluminum there result inexpensive lightaluminum base alloys, which, when heattreated in a particular mannerdiscovered by us, possess materially higher physical properties thanpreviously known similar aluminum-beryllium alloys. As to thisheattreatment. we have discovered that aluminum-beryllium alloys,particularly when made 'from quite pure metals, possess a markedincrease in hardness and tensile strength when heated for a substantialperiod of time at a temperature slightly below the aluminum-berylliumeutectic temperature and then quenched in water or another suitablequenching medium. We have also discovered that aluminum-beryllium alloyswhen thus heat-treated, age harden, both naturally at room temperatures,at v temperatures not higher than about 200C.

In the practice of the feature of our invention having to do with amethod of heattreating aluminum base alloys containing beryllium, suchan alloy is heated to a temperature slightly below the melting point ofthe most fusible constituent of the alloy. which may be that of thealuminum-beryllium eutectic, and is maintained at such temperature for asubstantial period of time, the alloy being then quenched at, orsubstantially at, the temperature to which it was heated. -We have foundthat the temperature to which the alloy is heated and at which it ismaintained may vary from about 550 C. to slightly below 645 C., whichlatter and artificially is about the alu-- Application filed November22, 1926. Serial No. 150,141.

,minum-beryl'lium eutectic temperature. The period of time during whichthe alloy is maintained at an elevated temperature varies with its sizeand with the heating tem erature and the beryllium content of the al 0y.The time of heat-treatment will also vary according as the alloy is inthe cast condition or has higher than about 200 C. We have found that analuminumberyllium alloy. for example a binary alloy in the form of acasting, a'ge hardens naturally at room temperature quite rapidly, andthat this hardening is often substantially complete after one or twodays. However, feet the age hardening artificially at elevatedtemperatures.

As has been stated, the effect of this-heattreatment is to substantiallyincrease the hardness and tensile strength of the alloy. As cast, thealloy may contain undissolved beryllium, which, upon being heated in themanner explained, tends to dissolve and form a solid solution up to thesolubility limit at the temperature to whichit is heated. \Vhen thealloy is quenched from this temperature the solid solution is retainedat room temper ature, and, upon aging. the out which was dissolved atthe higher temperature tends to precipitate in the form of very' smallparticles which harden and stiffen the matrix, thereby increasing thestrength and hardness of the alloy.

Aluminum-beryllium alloys such as herein contemplated may be variouslymanufactured. For example, an alloy of low beryllium content may beprepared by stirring metallic beryllium, which melts at about 1280 C. inmolten aluminum at about 1100 C. until the beryllium is dissolved. Theuse of small amounts. of a flux such as barium chloride facilitatesintroduction of the beryllium. By using higher temperatures, richaluminumberyllium alloys containing 10, 25 or per cent or more ofberyllium may be prepared it is sometimes advantageous to ef excessconstituselves without subsequent alloyin in this way for use in thesubsequent preparation of aluminum-beryllium alloys having lowerberyllium content, or for use themalloys in iron molds to give chillcast slabs about one-fourth of an inch thick. The Brinell hardnessvalues of these alloys as cast were determined by usin a 10 millimeterball under a load of 500 kilograms, and are give in the second column ofthe table. The several specimens were then all heated for 24 hours at atemperature of 631 C. and then quenched in water, after which theirBrinell hardness values given in the third column of the table weredetermined in the manner just explained. Thereafter the specimens wereall permitted to age naturally for'two days at roBm temperature, andtheir Brinell hardness values given in the last column of the table werethen determined.

-Hardness Berylli- Hard- Hard- 13, um ness ness 2 a per cent as castquenched at g temperature This table shows that the Brinell hardnessvalues of the specimen containing 013% beryllium do not vary materiallywith .heattreatment, the hardness value of the specimen when quenchedand aged being substantially the same as when cast. However, thespecimen having a beryllium content of 025% when quenched and aged had aBrinell hardness materially higher than as cast or as quenched, and thisis likewise true of the several specimens having beryllium contentsgreater than 025%. From this it appears that aluminum base alloyscontaining not less than about 025% beryllium are capable of havingtheir hardness and strength substantially increased by heat-treatingthem according to this invention. I

Several tests were madeto determine the effect of heating the alloys attemperatures above and below that used in heating the specimens given inthe above table. A specimen of an alloy containing .07 5% beryllium-"after being heated for 18 hours at 037 (3., .65

quenchedin water airdiged three days at room temperature was found tohave a Brinell hardness of 24 immediately after quenching, and of 45after aging. Other specimens of the same alloy after being ,heated for18 hours at 600 C. and quenched in water were found to have an averageBrinell hardness value of 25 as quenched, and of 40.2 after ag-' ing atroom temperature, showing a decrease in Brinell hardness as compared tothe sample which was heated at 637 C. but nevertheless shov'ing asubstantial increase in hardness as comparedto that as quenched.

Still further samples of the same aluminum-beryllium alloy after beingheated for 18 hours at 600 C. and quenched in water were found to have aBrinell hardness of 25.4. One sample was artificially aged for threehours at 150 C. and found to then have a Brinell hardness of 34.4.Another sample showed a Brinell hardness of only 27.1 after aging 50hours at room temperature, showing that the age hardening is more rapidat elevated than at room temperatures. V

Similar tests have been made of various other alloys containingdifferent percentages of beryllium with results of the same generalorder as typified by the examples just explained. As showing that theinvention. is applicable to aluminum-beryllium alloys containing muchlarger percentages of beryllium, an alloy containing. 23% berylliumafter being heated for 18 hours at 638 C. and quenched in water wasfound tohave a Brinell hardness of 30, and after being aged for two daysat room temperature the Brinell hardness was found to be 38.

The invention is applicable not only to chill castings made ofaluminum-beryllium alloys, but also to sand castings, as shown by thefolf lowing example. Samples of sand cast aluminum-beryllium alloyscontaining .5% beryllium showed in the cast condition an average tensilestrength of about 12,000 pounds per square inch and a Brinell hardnessof 21. After aging 11 days at room temperature the samples showed noappreciable change in strength or hardness. Other samples of the samealloy after being heated for 30 hours at 632 C. and quenched in waterhad a tensile strength of 13,000 pounds per square inch and a Brinellhardness of 23. These heat'- treated samples were then permitted to agenaturally at room temperature for 11 days, when it was found that theiraverage tensile strength was 17,000 pounds per square inch and theirBrinell hardness 36.

The samples thus far given have been of cast aluminum-beryllium alloys,but the invention contemplates wrought, rolled or otherwise workedalloys. As illustrative of this, an alloy containing 0.075% berylliumwas forged hot to a bar about five-eighths of an inch square, and afterannealin was found to have a Brinell hardness o 16.4. The sample wasthen heated for 20 hours at 0 beryllium, ranging from 0.0125 to 23.0

per cent, using aluminum of about 99.9% purity. We found that sheet0.064 inches thick can be rolled readily from small ingots of thesealloys. Two samples illustrative of the beneficial effect of our heattreatv ment upon sheet material 0.064 inches thick are given in thefollowing table.

Annealed state lleat tmated state 7 a; Beryllium per cent Yield TensileElonga- Yield Tensile Elongapoint strength tion point strength tion Inthis table the sheet in its annealed state had been annealed at 300 0.,and in its heattreated state it had been heated for one and one-halfhours at 625 (1., quenched in cold water, and aged several weeks at roomtems perature. The yield points and tensile strengths are given inpounds per square inch, and the elongations in per cents in two inches.

Heat-treatment of aluminum-beryllium alloy sheet also serves to increasethe corrosion resistance as determined by the usual salt spray method.In applying this test the changes in elongation are usually consideredto constitute a more sensitive criterion of the corrosion effect thanthe changes in tensile strength. Samples of sheet rolled from thealuminum-beryl]imn alloy were exposed to salt spray for 1300 hours, withthe followspecimens are much less affected by the salt spray than sheetswhich are in the as rolled or annealed condition.

As previously indicated, a further feature of our'invention has to dowith the provision of ternary or 'more complex aluminum alloyscontaining beryllium. We have found very useful and beneficial effectsare produced by the addition of beryllium to aluminum base alloyscontaining silicon, copper, magnesium, magnesium and silicon, magnesiumand copper, and magnesium, copper and silicon. Depending upon theparticular alloy in question, the effect of the addition of beryllium tothese alloys may, for example, be to confer age hardeningcharactertistics where they did not exist before, to increase the agehardening characteristics already inherent in the alloy, and to increasethe total hardness of the alloy. v I As shown by the following example,beryllium confers age-hardening properties upon chill castaluminum-copper alloys. Such an alloy containing 4% copper and noberyllium after being chill cast showed no appreciable increase inhardness after standing several days at room temperature. However, when05% of beryllium was added to an aluminum base alloy containing 4%copper and the alloy chill cast, the Brinell hardness increased from 46immediately after casting to 69 after the sample was aged naturally forfive days at room temperature Similarly, the Brinell hardness of analuminum alloy containing 3% copper and 0.05% beryllium increased from48 as cast to 64 after aging eight days at room temperature. Afterheating samples of the last mentioned aluminum-coppercontent of otheraluminum base alloys containing these constituents.

Heat-treated pure aluminum-copper alloys show distinct hardening at roomtemperature. For example, an aluminum-copper alloy containing 4% copperwas heat-treated at 550 C. and quenched. The hardness of the as quenchedspecimen was 63. After aging twenty-five days at room temperature, thehardness had increased to 79. The addition of beryllium to such an alloycauses an increase in this effect. The addition of 0.05% beryllium tothe foregoing alloy caused the hardness to increase from 65 immediatelyafter quenching from 550 C. to 99 after aging twenty-five days at roomtemperature.

It is shown in the following example that 'the addition of beryllium toaluminium-coplltl taining 6% copper and the resulting alloy treatingperiods much shorter than some of those used in the preceding examplesproduce equally beneficial results. As illustrative of this, samples ofa forged aluminumcopper-beryllium alloy containing 6% cop'- per and .81beryllium-were heat-treated for two and one-half hours at 554 C. andquenched in water. As determined by using a 1000 kilogram load, theBrinell hardness of this alloy as quenched was 69, and after agingnaturally at room temperature for twentyfour hours it had risen to 98.At the end of forty-eight hours the Brinell hardness was 99, and at theend of twelve days it was 101. The average tensile strength of for edsamples of this alloy after aging twelve ays was found to be about52,000 pounds per square inch, and the elongation to be 25% in twoinches.

As to the effects of beryllium on aluminum base alloys containingadditional allo ing constituents other than copper, we lave found by anumber of tests that the addition of silicon to aluminum berylliumalloys results in an increase of their final hardness after quenching.An aluminum base alloy containing .1% beryllium, .5% magnesium and 1%silicon was found to have a Brinell hardness of 42 as cast and of 54after aging for one week at room temperatures, the latter beingmaterially higher than that of a similar alloy not containing beryllium.After being heated for eighteen hours at 550 0., quenched in water andaged for one week at room temperature the Brinell hardness of thealuminum-beryllium-magnesium-silicon alloyjust described was found to be74. An alloy of the same compositionplus 4% copper showed as cast aBrinell hardness of 70, and after aging at room-temperature for one weekit showed a Brinell hardness of 84. Samples of this alloy, after beingheated for fifty hours at 500 C. and quenched in water, sh0wed asquenched a Brinell hard-.

I ness of 57, and after aging at room tempera-.

ture for one week a Brinell hardness of 97.

From the foregoing it clearly appears that certain aluminum base alloyscontaining beryllium, whether they are binary, ternary or more complexalloys, have their physical properties substantially increased byheating them for a substantial period at a-temperature slightly belowthe melting point of the scribed.

aluminum-beryllium eutectic, or in the case of the ternary and morecomplex alloys to a temperature slightly below the melting point of themost fusible constituent of the alloys,

and then quenching them. In general, regardless of the temperature atwhich an aluminum-beryllium alloy may be treated, it is necessary toheat the alloy only long enough to cause substantial solutionof theundissolved beryllium constituent. It is also evident from the foregoingexamples of aluminum base ternary and more complex 4 alloys containingberyllium that theypossess are heat-treated acco i'ding to the methodhere provided. When it is desired to age the heat:

substantial advanta es whether or not they treated alloys at elevatedtemperatures, it is possible to quench them from the heat ,treatii'igtemperature in boiling water or other suitable medium at the desiredtemperature and to maintain them at this temperature for an appropriatelength of time.

' Throughout this specification, and in the appended claims, theexpression aluminum base alloy is used to describe an alloy in whichaluminum is the predominant constituent regardless of whether the alloyis binary, ternary, or of a more complex order. No claim-is made in thisapplication to the improved alloys which we have disclosed, such alloysbeing claimed in a divisional application. I

According to the provisions of the patent statutes, we have explainedthe principle and mode of operation of our invention and have describednumerous specific examples of the manner in which it may be practiced.However, we desire to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than asexplained with reference to' the examples given, and in alloys havingcompositions differing from those particularly de- We claim asburinvention: 1. The metliod of treating an aluminum base alloy containingberyllium, which com-' prises 'heating the alloy to a temperatureslightly below themelt-ing point of the aluminum-beryllium eutectic tocause substantial solution of the-undissolved beryllium constituent ofthe alloy, and thereafter quenching the alloyfrom substantially saidtemperature.

2. The method of treating an aluminum base alloy containing not-lessthan about 025% beryllium, which comprises heating the alloy to atemperature slightly below;'

the melting point. of the most fusible constituent of the alloyto causesubstantial solution of the undissolved beryllium constituent of thealloy, and thereafter quenching the alloy from substantially saidtemperature.

3. The method of treating an aluminum basealloy containing from about.025 to 1.00% beryllium, which comprises heating the alloy to atemperature slightly below the base alloy containing from about .025 to'25.0% beryllium, which comprises heating the alloy to a temperatureslightly below the melting point of the most fusible constituent of thealloy to cause substantial solution of the undissolved berylliumconstituent of the alloy, and thereafter quenching the alloy fromsubstantially said temperature.

5. The method of treating an aluminum base alloy containing beryllium,which comprises heating the alloy to a temperature slightly below themelting point of the alui'nihum-beryllium eutectic to cause substantialsolution of the undissolved beryllium constituent of the alloy,thereafter quenching the alloy from substantially said temperature. andsubsequently aging the alloy at a tem perature not higher than about 200C.

(5. The method of treating an aluminum base alloy containing not lessthan about .025% beryllium, which comprises heating the. alloy to atemperature slightly below the melting point of the most fusibleconstituent of the alloy to cause substantial solution of theundissolved beryllium constituent of the alloy, thereafter quenching thealloy from substantially said temperature, and subsequently aging thealloy at a temperature not higher than about 200 C. p

7. The method of treating an aluminum base alloy containing from about.025 to 1.00% beryllium, which comprises heating the alloy to atemperature slightly below the melting point of the most fusibleconstituent of the alloy to cause substantial solution of theundissolved beryllium constituent of the alloy, thereafter quenching thealloy from substantially said temperature, and subsequently aging thealloy at a temperature not higher than about 200 C.

8. The method of treating an aluminum base alloy containing from about.025 to! 25.0% beryllium, which comprises heating the alloy to atemperature slightly below the melting point of the most fusibleconstituent of the alloy to cause substantial solution of theundissolved beryllium constituent of the alloy, thereafter quenching thealloy from substantially said temperature, and subsequently-aging thealloy at a temperature not higher than about 200 C.

9. The method of treating an aluminum base alloy containing not lessthan about .025% beryllium and also containing copper, which comprisesheating the alloy to a temperature slightly below the melting point ofthemost fusible constituent of the alloy to cause substantial solutionof the undissolved beryllium constituent of the alloy, and thereafterquenching the alloy from substantially said temperature.

10. The method of treating an aluminum base alloy containing not lessthan about 025% beryllium and also containing silicon and copper, whichcomprises heating the alloy to a temperature slightly below the meltingpoint of the most fusible constituent of the alloy to cause substantialsolution of the undissolved beryllium constituent of the alloy, andthereafter quenching the alloy from substantially said temperature.

11. The method of increasing the hardness and tensile strength of analuminum base alloy containing not less than 025% beryllium, whichcomprises heating the alloy to a temperature below the melting point ofits most fusible constituent, and thereafter quenching the alloy fromsubstantially said temperature.

In testimony whereof, We hereunto sign our names.

ROBERT S. ARCHER. .\VILLIA1\I'L. FINK.

